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                  <p class="p_Heading1"><span class="f_Heading1">Interface</span></p>



  
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                <p class="p_TextIndentedL2"><img src="d_interface.png" width="84" height="87" border="0" alt="d_Interface"></p>
<p class="p_BodyText"><span class="f_BodyText">An </span><span class="f_BodyText" style="font-style: italic;">Interface</span><span class="f_BodyText"> is a specification of behavior (or contract) that implementers agree to meet. By implementing an Interface, </span><span class="f_BodyText" style="font-style: italic;"><a href="classdiagram.htm">Classes</a></span><span class="f_BodyText"> are guaranteed to support a required behavior, which enables the system to treat non-related elements in the same way; that is, through the common interface. You also use Interfaces in a <a href="compositestructurediagram.htm">Composite Structure</a> diagram.</span></p>
<p class="p_BodyText"><span class="f_BodyText">Interfaces are drawn in a similar way to a <a href="class.htm">Class</a>, with operations specified, as shown below. They can also be drawn as a circle with no explicit operations detailed. Use the right-click context menu option </span><span class="f_MenuKeyField">Use Circle Notation</span><span class="f_BodyText"> to switch between styles. <a href="realise.htm">Realization</a> connectors to an Interface drawn as a circle are drawn as a solid line without target arrows.</span></p>
<p class="p_TextIndentedL2"><img src="interface.png" width="257" height="115" border="0" alt="Interface"></p>
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<td valign="bottom" width="955" bgcolor="#efeff7" style="width:955px; background-color:#efeff7;"><p class="p_TiporNote" style="border-top: none; border-right: none; border-left: none;"><span class="f_TiporNote">Note:</span></p>
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<td width="955" bgcolor="#f7f7ff" style="width:955px; background-color:#f7f7ff;"><p class="p_TiporNoteText"><span class="f_TiporNoteText">An Interface cannot be instantiated (that is, you cannot create an object from an Interface). You must create a Class that 'implements' the Interface specification, and in the Class body place operations for each of the Interface operations. You can then instantiate the Class.</span></p>
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<p class="p_SubHeadingL1"><span class="f_SubHeadingL1">Toolbox Icon</span></p>
<p class="p_TextIndentedL2"><img src="e_interface.png" width="168" height="24" border="0" alt="e_Interface"></p>
<p class="p_SubHeadingL1"><span class="f_SubHeadingL1">OMG UML Specification</span></p>
<p class="p_BodyText"><span class="f_BodyText">The OMG UML specification (</span><span class="f_BodyText" style="font-style: italic;">UML Superstructure Specification, v2.1.1, p. 88</span><span class="f_BodyText">) states:</span></p>
<p class="p_OMGText"><span class="f_OMGText">An interface is a kind of classifier that represents a declaration of a set of coherent public features and obligations. An interface specifies a contract; any instance of a classifier that realizes the interface must fulfill that contract. The obligations that may be associated with an interface are in the form of various kinds of constraints (such as pre- and post-conditions) or protocol specifications, which may impose ordering restrictions on interactions through the interface.</span></p>
<p class="p_OMGText"><span class="f_OMGText">Since interfaces are declarations, they are not instantiable. Instead, an interface specification is implemented by an instance of an instantiable classifier, which means that the instantiable classifier presents a public facade that conforms to the interface specification. Note that a given classifier may implement more than one interface and that an interface may be implemented by a number of different classifiers.</span></p>




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